Pneumatic cylinders



Feb. 14, 1967 R. E. GEEsoN 3,303,756

PNEUMATIC CYLINDERS I Filed Dec. 4, 1964 3 Sheets-Sheet 1 EH Lk T v Q5nvenlor 2705er? ErfLeJZ 'ee'aru.

Feb- 14, 1957 R. E. GEEsoN PNEUMATIC CYLINDERS 5 Sheets-Sheet 2 FiledDec. 4, 1964 n venlor OZ er? Em esi 02295071/ Feb. 14, 1967 R, E.GEL-:SON

PNEUMATIC CYLINDERS 3 Sheets-Sheet 3 Filed DSG. 4, 1964 Inventor I@27er? Erfzf 6565070.

By aj/m, ff-L, wmf/@1% United States Patent 3,303,756 PNEUMATICCYLINDERS Robert Ernest Geeson, Croydon, England, assigner to The MetalBox Company Limited, London, England, a British company Filed Dec. 4,1964, Ser. No. 416,052 Claims priority, application Great Britain, Dec.4, 1963, 47,966/ 63 11 Claims. (Cl. 92--85) This invention relates topneumatic cylinders.

As is well understood a mechanism operated by a pneumatic cylinder cansometimes be arranged to limit the travel of the operating piston ateach end of the stroke thereof and this is sometimes effected bypermitting metallic contact with the cylinder end covers. This, however,results in an undesirable volume of noise and shock loads on thecomponents of the cylinder and the mechanism operated thereby and suchloads are conducive of fatigue failures.

It is also known that a desirable cushioning effect can be provided forlong-stroke cylinders by using truncated pistons with projectingportions on both sides of the main portion of the piston, suchprojecting portions having diameters substantially smaller than that ofsaid main portion. These projecting portions are arranged to entercavities in the cylinder end covers prior to the main portion of thepiston reaching the end of its stroke. Air thus entrapped in suchcavities becomes pressurised to a degree suflicient to cause the pistontravel to be retarded smoothly to rest. A controlled release of pressurefrom the cavities is usually provided to ensure that completion of thestroke is effected.

When the pneumatic cylinder is a short-stroke cylinder, particularly acylinder having a working stroke which is shorter than the internaldiameter of the cylinder, it is not possible to use the cushioningmethods which can be used with long-stroke cylinders and it is an objectof the present invention to provide a short-stroke pneumatic cylinderwith adequate cushioning means.

According to the invention there is provided a pneumatic cylindercomprising an operating piston movable axially in a housing in responseto air pressure admitted to the housing and having a stroke the lengthof which is less than the internal diameter of the housing, a piston rodmovable axially with the operating piston and arranged for connectionwith a member to be operated thereby, and a cushioning device externalof said housing and comprising a cushioning piston movable axially in acushioning chamber in response to movement of the operating piston, saidcushioning chamber being provided at each of the opposite ends thereofwith a shallow recess into which the cushioning piston is moved at itapproaches an end of the stroke thereof thereby to cornpress air in therecess to retard and arrest movement of the operating piston before itengages the end of the housing, and openings in the side of thecushioning chamber to maintain at atmospheric pressure that portion ofthe cushioning chamber which is behind the cushioning piston as itenters one of the shallow recesses. The diameter of the cushioningpiston is preferably substantially equal to or is greater than that ofthe operating piston.

The diameter of the cushioning piston may be slightly less than theinternal diameter of said recess thereby to permit air entrapped as thecushioning piston approaches the end of a recess to escape slowly aroundthe cushioning piston while permitting the cushioning piston to reacnthe full extent of the stroke thereof.

In one embodiment of the invention the cushioning chamber is formed by abody portion and a co-axial chamber cover retained in spaced axialrelation by a sleeve tted over spigots extending respectively from thebody portion and the chamber cover, said sleeve having an internal wallwhich is interrupted between the ends of the sleeve to provide at theends thereof continuous wall portions which extend from the end faces ofsaid spigots and dene the axial length of the shallow recesses. Theinterruption may be formed by ports extending radially through the sidesof the sleeve. Alternatively, the interruption may be formed by anannular groove formed in the sleeve and ports which extend from thegroove to the exterior of the sleeve.

In another embodiment of the invention the cushioning chamber is formedby a body portion and a co-axial chamber cover located in spaced axialrelation by a sleeve co-axial with and rotatable about the axis of thechamber and provided with left and right hand internal screw threadsspaced apart axially of the sleeve, said body portion and chamber coverhaving spigots of lesser external diameter than the internal diameter ofthe sleeve and the end faces of which are directed towards each other toform the opposite ends of the cushioning chamber, and left and righthand rings slidable axially in the annular spaces formed between thesleeve and spigots and provided respectively with left and right handexternal screw threads which mesh with the like internal threadsprovided on the sleeve, the inner walls of the rings extending beyondthe end faces of the spigots to form said recesses therewith, the axiallength of the recesses being adjustable by rotation of the sleeve andatmospheric air admissible to the cushioning chamber through radialports formed in the sleeve between the position of location of saidinternal screw threads.

The housing may be formed by a cylinder one end of which is screwed intosaid body portion of the cushioning chamber on the side thereof oppositethat `on which the spigot is formed, and the opposite end of thecylinder is screwed into a housing end cover, and the operating andcushioning pistons are arranged each to be movable axially with thepiston rod. The cushioning piston may be integral with a sleeve co-axialwith and connected to the piston rod and the cushioning piston be guidedfor axial movement by a projection co-axial therewith and extending fromthe chamber cover.

In order that the invention may be clearly understood some embodimentsthereof will now be described, by way of example, with reference to theaccompanying drawings, in which:

FIGURE 1 is a longitudinal section through a pneumatic cylinderaccording to the invention,

FIGURE 2 is a view of a part of FIGURE 1 showing a modification thereto,

FIGURE 3 is a longitudinal section through an alternative form ofpneumatic cylinder according to the invention,

FIGURE 4 is a section of a part of a pneumatic cylinder and illustratesan alternative form of cushioning chamber which can be employedtherewith, and

FIGURE 5 is a longitudinal section through another alternative form ofpneumatic cylinder according to the invention.

In the drawings like or similar parts are indicated by like referencenumerals.

Referring to FIGURE l, the pneumatic cylinder comprises an operatingpiston 1, of known construction, movable axially in a housing 2 inresponse to air pressure admitted to the housing through ports 3, 4according to the direction of movement of the piston. The piston 1 has astroke the length of which is less than the intern-al diameter of thehousing 2. A piston rod 5 is movable axially with the operating piston 1and is arranged for c-onnection, `as by a screw threaded end 6, with amember 7 Ito be operated thereby. As shown in the drawings, the housingis formed by a cylinder 8 and one end 3 9 of which is screwed into thebody portion 10 of a cushioning chamber, to be described below, an-d theopposite end 11 of cylinder 8 is screwed into a housing end cover 12.

External of the housing 2 there is provided a cushioning devicecomprising a cushioning piston 13 movable axially in a cushioningchamber 14 in response to movement of the operating piston 1. Thecushioning chamber is provided at each of the opposite ends thereof witha shallow recess 15 into which the cushioning piston 13 is moved as itapproaches an end of the stroke thereof thereby to compress air in therecess to retard and arrest movement of the operating piston 1 before itengages the end of the housing 2. Openings, shown as ports 16, in theside of the cushioning chamber 14 maintain at atmospheric pressure thatportion of the cushioning chamber which is behind the cushioning pist-on13 as it enters one of the shallow recesses 15. The diameter of thecushioning piston 13 is substantially eq-ual to or is greater than thatof the -operating piston 1 and the arrangement is such that the whole ofthe area of a face of the cushioning piston 13 can come into closecontact with the ends of the recesses 15 at the ends of the stroke ofthe cushioning piston.

The diameter of the cushioning piston 13 is slightly less than theinternal diameter of the recesses 15 so as to permit air entrapped asthe cushioning piston approaches the end of a recess to escape slowlyaround the cushioning piston while permitting the cushioning pist-on toreach the full extent of the stroke thereof. In the embodiment of theinvention illustrated in FIGURE 1 the piston rod is a close sliding t inbearings 17, 18 and the diameter of the cushioning piston 13 is suchthat it will not usually be tit-ted with sealing devices.

The cushioning chamber 14 is formed by the `body portion and a co-axialchamber cover 19 retained in spaced axial relation by a sleeve 20 tittedover spigots 21, 22 extending respectively lfrom the body portion 10 andthe chamber cover 19 an-d the sleeve 20 has an internal wall which isinterrupted between the ends of the sleeve to provide at the endsthereof continuous Wall portions 23 which extend from the end faces ofthe spigots 21, 212 and define the axial length of the shallow recesses15. As shown in FIGURsE 1 the interruption is formed by the ports 16which ex-tend radially through the sides of the sleeve but in themodified embodiment of the invention shown in FIGURE 2 the interruptionis formed by an annular groove 24 and ports 16a extend from the groove24 t-o the exterior of the sleeve.

`In the alternative form of pneumatic cylinder shown in FIGURE 3 thecushioning piston 1-3 is integral with a sleeve 215 co-axial with andconnected to the piston rod `5 and the cushioning piston is guided foraxial movement by a projection 26 co-axial therewith and extending fromthe chamber cover 19.

FIGUR'E 4 illustrates a modified form of cushioning chamber in which asleeve 20a locates the body portion 10 and chamber cover 19 in axialspaced relation. The sleeve 20a is rotatable about the axis of thecushioning chamber and is provided with left and right hand internalscrew threads 27, 28 spaced apart axially of the sleeve. The end coveris retained in position by bolts 29 extending through distance pieces 30and the sleeve 20a is normally restrained against rotation by a clampingmember 31. The body portion 10 and chamber cover 19 respectively Ihavespigots 32, 33 of lesser external diameter than the internal diameter ofthe sleeve 20a and the end faces of the spigots are directed towardseach other to for-m the opposite ends of the cushioning chamber. Leftand right hand rings 34, 35 are slidable axially in Ithe annular spacesformed between the sleeve 20a and spigots 32, 33 and are providedrespectively with left and right hand external screw threads which meshwith the ylike inte-rnal threads provided on the sleeve 20a. The innerwalls of the rings 34, 35 extend beyond the end faces of the spigots 32,33 to form therewith recesses 15. By releasing the clamping member 31the sleeve 20a can be rotated and thus affect adjustment of the axiallength of the recesses 15 by effecting axial movement of the ringssimultaneously in opposite directions. In this ernbodiment of theinvention atmospheric air is admissible to the cushioning chamberthrough ports 16b formed in the sleeve 20a between the positions oflocations of the internal screw threads 27, Z8.

In each of the embodiments of the invention the cushioning chamber 14 isprovided with ports 16, 16a or 16b so that when the cushioning piston 13is in close contact with an end ofthe cham-ber atmospheric air isallowed to enter the chamber at the opposite side of the piston. Thedimensions of the ports are so proportioned in respect of the workingpressure of the operating cylinder an-d the mass of the -moving partsthat shortly before each end of the stroke la volume of atmospheric airis entrapped by the cushioning piston 13 in a recess 15. This volume ofair is selected to be suflicient to retard movement of the operatingpiston 1 so that the mechanism is arrested without violent impact, theclearance around the piston enabling the entrapped air to escape slowlyenough to achieve this object without preventing the cushioning pistonfrom reaching the full extent of its stroke.

As described above the cushioning chamber 14 is integral with, butexternal of, the housing 2 but if desired the cushioning chamber 19 maybe separate from the housing 2 as shown in FIGURE 5. When the chamber 14is integral with the housing 2 the pistons 1 and 13 are convenientlyboth movable with the piston rod 5 but if the chamber 14 is separatefrom housing 2 a piston rod for the piston 13 may be attached to thepiston rod for piston 1 or to some convenient part of the member 7operated by the piston 1 as shown in FIGURE 5.

I claim:

1. A pneumatic cylinder comprising an operating piston movable axiallyin a housing in response to air pressure admitted to the housing andhaving a stroke the length of which is less than the internal diameterof the housing, a piston rod movable axially with the operating pistonand arranged for connection with a member to be operated thereby, and acushioning device external of said housing and comprising a cushioningpiston movable axially in a cushioning chamber in response to movementof the operating piston, said cushioning chamber being provided at eachof the opposite ends thereof with a shallow recess into which thecushioning piston is moved as'it approaches an end of the stroke thereofthereby to compress air in the recess to retard and arrest movement ofthe operating piston before it engages the end of the housing, andopenings in theside of the cushioning chamber to maint-ain atatmospheric pressure that portion of the cushioning chamber which isbehind the cushioning piston as it enters one of the shallow recesses.

2. A pneumatic cylinder according to claim 1, wherein the diameter ofthe cushioning piston is substantially equal to or is greater than thatofthe operating piston.

3. A pneumatic cylinder according to claim 1, wherein the diameter ofthe cushioning piston is slightly less than the internal diameter ofsaid recesses thereby to permit air entrapped as the cushioning pistonapproaches the end of a recess to escape slowly around the cushioningpiston while permitting the cushioning piston to reach the full extentof the stroke thereof.

4. A pneumatic cylinder according to claim 1, wherein the cushioning-chamber is formed by .a body portion and a co-axial chamber coverretained in spaced axial relation by a sleeve iitted over spigotsextending respectively from the body portion and the chamber cover, saidsleeve having an internal wall which is interrupted between the ends ofthe sleeve to provide at the ends thereof continuous wall portions whichextend from the end faces of the said spigots and define the axiallength of the shallow recesses.

5. A pneumatic cylinder according to claim 4, wherein the interruptionis formed by ports extending radially through the sides of the sleeve.

6. A pneumatic cylinder according to claim 4, wherein the interruptionis formed by an annular groove formed in the sleeve and ports extendfrom the groove to the exterior of the sleeve.

7. A pneumatic cylinder according to claim 1, wherein the cushioningchamber is formed by a body portion and a co-axial chamber cover locatedin spaced axial relation by a sleeve co-axial with and rotatable yaboutthe axis of the chamber and provided with left and right hand internalscrew threads spaced apart axially of the sleeve, said body portion andchamber cover having spigots of lesser external diameter than theinternal diameter of the sleeve and the end faces of which are directedtowards each other to form the opposite ends of the cushioning chamber,and left and right hand rings slidable axially in the annular spacesformed between the sleeve and spigots and provided respec-tively withleft and right hand external screw threads which mesh with the likeinternal threads provided on the sleeve, the inner walls ofthe ringsextending beyond the end faces of the spigots to form said recessestherewith, the axial length of the recesses being adjustable by rotationof the sleeve and atmospheric air admissible to the cushioning chamberthrough radial ports formed in the sleeve between the positions oflocation of said internal screw threads.

8. A pneumatic cylinder according to claim 7, wherein the housing isformed by a cylinder one end of which is screwed into said body portionof the cushioning chamber on the side thereof opposite that on which thespigot is formed, and the opposite end of the cylinder is screwed into.a housing end cover, and wherein the operating and cushioning pistonsare each movable axially with the piston rod.

9. A pneumatic cylinder according to claim 7, wherein the cushioningpist-on is integral with a sleeve co-axial with and connected to thepiston rod and the cushioning piston is guided for axial movement by aprojection coaxial therewith yand extending from the chamber cover.

10. A pneumatic cylinder according to claim 4, wherein the housing isformed by a cylinder, one end of which is screwed into said body portionof the cushioning chamber on the side thereof opposite that on which thespigot is formed, and the opposite end of the cylinder is screwed into ahousing end cover, and wherein the operating and cushioning pistons areeach movable -axially with the piston rod.

11. A pneumatic cylinder .according to claim 4 wherein the cushioningpiston is integral with a sleeve coaxial with and connected to thepiston rod and the cushioning piston is guided for axial movement by aprojection coaxial therewith and extending from the chamber cover.

References Cited by the Examiner UNITED STATES PATENTS 364,081 5/1887Bates 92-85 X 859,629 7/1907 Symons et al 92-85 X 1,077,781 11/1913Yeager 18S-88.1 1,522,243 1/1925 Hughes 18S-88.1 2,815,004 12/1957Droman 92-85 FOREIGN PATENTS 1,267,211 6/ 1961 France.

MARTIN P. SCHWADRON, Primary Examiner.

I. C. COHEN, Assistant Examiner.

1. A PNEUMATIC CYLINDER COMPRISING AN OPERATING PISTON MOVABLE AXIALLYIN A HOUSING IN RESPONSE TO AIR PRESSURE ADMITTED TO THE HOUSING ANDHAVING A STROKE THE LENGTH OF WHICH IS LESS THAN THE INTERNAL DIAMETEROF THE HOUSING, A PISTON ROD MOVABLE AXIALLY WITH THE OPERATING PISTONAND ARRANGED FOR CONNECTION WITH A MEMBER TO BE OPERATED THEREBY, AND ACUSHIONING DEVICE EXTERNAL OF SAID HOUSING AND COMPRISING A CUSHIONINGPISTON MOVABLE AXIALLY IN A CUSHIONING CHAMBER IN RESPONSE TO MOVEMENTOF THE OPERATING PISTON, SAID CUSHIONING CHAMBER BEING PROVIDED AT EACHOF THE OPPOSITE ENDS THEREOF WITH A SHALLOW RECESS INTO WHICH THECUSHIONING PISTON IS MOVED AS IT APPROACHES AN END OF THE STROKE THEREOFTHEREBY TO COMPRESS AIR IN THE RECESS TO RETARD AND ARREST MOVEMENT OFTHE OPERATING PISTON BEFORE IT ENGAGES THE END OF THE HOUSING, ANDOPENINGS IN THE SIDE OF THE CUSHIONING CHAMBER TO MAINTAIN ATATMOSPHERIC PRESSURE THAT PORTION OF THE CUSHIONING CHAMBER WHICH ISBEHIND THE CUSHIONING PISTON AS IT ENTERS ONE OF THE SHALLOW RECESSES.